We are experimenting with different biological materials that are suitable for structural analysis by tomography. At the same time, we are looking for specimens that will serve as good test structures for evaluating different practical and computational approaches to tomographic reconstruction. Our greatest experience so far is with the Golgi apparatus in cultured rat cells (see collaboration with Kathryn Howell). We have also experimented with fixed, embedded insect flight muscle as a specimen with which to evaluate different algorithms for tomographic reconstruction. This work has demonstrated the importance of including tilts around two orthogonal axes to improve the isotrophy of both resolution and contrast. Since this implies as many as 240 images for a single tomogram, we have also investigated algorithms for sampling 3-dimensional Fourier space more efficiently. Mastronarde has shown that tilt increments defined by a cosine function provide a significant reduction in microscopy time and provide good isotropic resolution. These methods have now been applied to thick sections of anaphase chromosomes from PTK cells, and the methods used to reconstruct the interaction between microtubules, kinetochores, and centrosomes. Several unexpected features of the geometry of microtubule ends have been identified, thanks to the quality of the 3-dimensional images now available.